1. Field of Invention
The invention relates to a capacitor substrate and, in particular, to the structure of an interleaving striped capacitor substrate.
2. Related Art
The print circuit board for supporting electronic elements in normal electronic systems is usually a planar substrate of a single low dielectric coefficient material (such as glass fiber cloths). Its drawbacks are that the low dielectric coefficient material is not good at suppressing high-frequency noise and the integrity of passive elements on the print circuit board is poor. It is not ideal for modern electronic systems where high frequency, high speed and compactness are the basic requirements. Consequently, the print circuit board needs to be improved to suppress high-frequency noise, to enhance the integration of elements, and to reduce high-speed signal delays.
U.S. Pat. No. 5,161,086 provides an improved print circuit board to suppress high-frequency noise interference. In that patent, a conductive metal layer is attached to the upper and lower surfaces of a dielectric material layer to form a capacitor substrate. The capacitor substrate is stacked onto a print circuit board by pressing. Since each capacitor substrate has only one dielectric coefficient, if different capacitances are required (e.g., when one needs a low dielectric coefficient capacitor substrate for high-speed signal transmissions and a high dielectric coefficient capacitor substrate for the decoupling capacitor that suppresses high-frequency noise) one has to stack several capacitor substrates with different dielectric coefficients on the print circuit board.
The drawback of this method is that a single-layered capacitor substrate has only one dielectric coefficient that cannot simultaneously provide the capacitance properties required by a high-frequency and high-speed electronic system. In order to satisfy different electronic requirements, the cost of the print circuit board inevitably increases due to stacking multiple layers of capacitor substrates. For the mixed high-frequency analog and high-speed digital systems, the integrity of the added passive elements is still inadequate.
In addition, U.S. Pat. No. 4,759,965 provides a ceramic comprising two or more dielectric portions with different dielectric constants. However, according to the ceramic material used, it is difficult to manufacture a multi layered capacitor substrate and apply it to a large size substrate, so the highest capacitance that can be obtained is limited and the applications are restricted.
Furthermore, due to the ceramic material used, a high temperature sintering process is necessary for preparing a capacitor substrate. Therefore the cost is high.